import UIKit

enum RDEPUBTextRendererSupport {
    static func injectFragmentMarkers(into html: String) -> String {
        guard let regex = try? NSRegularExpression(pattern: #"(<[^>]+\sid="([^"]+)"[^>]*>)"#, options: [.caseInsensitive]) else {
            return html
        }
        return regex.stringByReplacingMatches(
            in: html,
            options: [],
            range: NSRange(location: 0, length: html.utf16.count),
            withTemplate: "${id=$2}$1"
        )
    }

    static func extractFragmentOffsets(from attributedString: NSMutableAttributedString) -> [String: Int] {
        let markerPattern = #"\$\{id=([^}]+)\}"#
        guard let regex = try? NSRegularExpression(pattern: markerPattern, options: []) else {
            return [:]
        }

        let mutableString = NSMutableString(string: attributedString.string)
        var fragmentOffsets: [String: Int] = [:]
        var searchRange = NSRange(location: 0, length: mutableString.length)
        var offsetAdjustment = 0

        while let match = regex.firstMatch(in: mutableString as String, options: [], range: searchRange) {
            let fullMatch = mutableString.substring(with: match.range) as NSString
            let fragmentID = fullMatch
                .replacingOccurrences(of: #"\$\{id="#, with: "", options: .regularExpression, range: NSRange(location: 0, length: fullMatch.length))
                .replacingOccurrences(of: #"\}"#, with: "", options: .regularExpression)

            let adjustedLocation = max(0, match.range.location + offsetAdjustment)
            fragmentOffsets[fragmentID] = adjustedLocation
            attributedString.deleteCharacters(in: match.range)
            mutableString.deleteCharacters(in: match.range)
            offsetAdjustment -= match.range.length
            searchRange = NSRange(location: match.range.location, length: mutableString.length - match.range.location)
        }

        return fragmentOffsets
    }

    static func normalizeReadingAttributes(in attributedString: NSMutableAttributedString, style: RDEPUBTextRenderStyle) {
        let fullRange = NSRange(location: 0, length: attributedString.length)
        attributedString.enumerateAttributes(in: fullRange) { attributes, range, _ in
            let sourceFont = attributes[.font] as? UIFont
            let paragraph = (attributes[.paragraphStyle] as? NSParagraphStyle)?.mutableCopy() as? NSMutableParagraphStyle ?? paragraphStyle(lineSpacing: style.lineSpacing)
            paragraph.lineSpacing = style.lineSpacing
            paragraph.paragraphSpacing = max(paragraph.paragraphSpacing, style.lineSpacing / 2)

            var updatedAttributes = attributes
            updatedAttributes[.font] = normalizedFont(from: sourceFont, baseFont: style.font)
            updatedAttributes[.paragraphStyle] = paragraph
            if let textColor = style.textColor {
                updatedAttributes[.foregroundColor] = textColor
            }
            attributedString.setAttributes(updatedAttributes, range: range)
        }
    }

    static func fallbackAttributedString(for html: String, style: RDEPUBTextRenderStyle) -> NSMutableAttributedString {
        let fallbackAttributes: [NSAttributedString.Key: Any] = [
            .font: style.font,
            .paragraphStyle: paragraphStyle(lineSpacing: style.lineSpacing),
            .foregroundColor: style.textColor ?? UIColor.black
        ]
        return NSMutableAttributedString(string: html, attributes: fallbackAttributes)
    }

    private static func normalizedFont(from sourceFont: UIFont?, baseFont: UIFont) -> UIFont {
        guard let sourceFont else {
            return baseFont
        }
        let traits = sourceFont.fontDescriptor.symbolicTraits.intersection([.traitBold, .traitItalic])
        if let descriptor = baseFont.fontDescriptor.withSymbolicTraits(traits) {
            return UIFont(descriptor: descriptor, size: baseFont.pointSize)
        }
        return baseFont
    }

    private static func paragraphStyle(lineSpacing: CGFloat) -> NSMutableParagraphStyle {
        let style = NSMutableParagraphStyle()
        style.lineSpacing = lineSpacing
        style.paragraphSpacing = max(6, lineSpacing / 2)
        return style
    }
}